Transmitting spread signal in communication system

ABSTRACT

The present invention provides for spreading a first signal using a plurality of spreading codes, multiplexing the first spread signal by code division multiplexing, transmitting the first multiplexed signal via a plurality of neighboring frequency resources of an OFDM symbol of a first antenna set, spreading a second signal using a plurality of spreading codes, multiplexing the second spread signal by code division multiplexing, transmitting the second multiplexed signal via a plurality of neighboring frequency resources of the OFDM symbol of the first antenna set, transmitting the first multiplexed signal via a plurality of neighboring frequency resources of an OFDM symbol of a second antenna set, and transmitting the second multiplexed signal via a plurality of neighboring frequency resources of the OFDM symbol of the second antenna set, wherein the first multiplexed signal is transmitted on frequency resources that neighbor frequency resources that the second multiplexed signal is transmitted on.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/849,759, filed on Aug. 3, 2010, which is a continuation of U.S.application Ser. No. 12/139,261, filed on Jun. 13, 2008, which claimsthe benefit of earlier filing date and right of priority to KoreanApplication No. 10-2008-0007935, filed on Jan. 25, 2008, and U.S.Provisional Application Nos. 60/943,783, filed on Jun. 13, 2007,60/955,019, filed on Aug. 9, 2007, 60/976,487, filed on Oct. 1, 2007,60/982,435, filed on Oct. 25, 2007, and 60/983,234, filed on Oct. 29,2007, the contents of which are hereby incorporated by reference hereinin their entirety.

FIELD OF THE INVENTION

The present invention relates to a mobile communication system, and moreparticularly, to transmitting a spread signal in a mobile communicationsystem.

BACKGROUND OF THE INVENTION

FIG. 1 illustrates an example of a conventional wireless (mobile)communication system. The wireless (mobile) communication system 100includes a plurality of Base Stations (BSs) 110 a, 110 b and 110 c and aplurality of User Equipments (UEs) 120 a to 120 i. Each BS 110 a, 110 bor 110 c provides services to its specific geographical area 102 a, 102b or 102 c, which may further be divided into a plurality of smallerareas 104 a, 104 b and 104 c. In a downlink, a transmitting end includesthe BS and a receiving end includes the UE. In an uplink, thetransmitting end includes the UE and the receiving end includes the BS.

Recently, the demand for wireless communication services has risenabruptly due to the generalization of information communicationservices, the advent of various multimedia services and the appearanceof high-quality services. To actively cope with the demand, acommunication system's capacity should first be increased. In order todo so, methods for finding new available frequency bands and raising theefficiency of given resources in wireless communication environments areconsidered.

Much effort and attention has been made to research and developmulti-antenna technology. Here, diversity gain is obtained byadditionally securing a spatial area for resource utilization with aplurality of antennas provided to a transceiver or raising transmissioncapacity by transmitting data in parallel via each antenna.

An example of a multi-antenna technology is a multiple input multipleoutput (MIMO) scheme. The MIMO scheme indicates an antenna system havingmultiple inputs and outputs, raises a quantity of information bytransmitting different information via each transmitting antenna, andenhances reliability of transport information using coding schemes suchas STC (space-time coding), STBC (space-time block coding), SFBC(space-frequency block coding) and the like.

SUMMARY OF THE INVENTION

The present invention is directed to transmitting a spread signal in amobile communication system.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, the presentinvention is embodied in a method for transmitting a spread signal in amobile communication system, the method comprising spreading a firstsignal using a plurality of spreading codes, wherein the plurality ofspreading codes have a spreading factor, multiplexing the first spreadsignal by code division multiplexing, transmitting the first multiplexedsignal via a plurality of neighboring frequency resources of an OFDMsymbol of a first antenna set, spreading a second signal using aplurality of spreading codes, wherein the plurality of spreading codeshave a spreading factor, multiplexing the second spread signal by codedivision multiplexing, transmitting the second multiplexed signal via aplurality of neighboring frequency resources of the OFDM symbol of thefirst antenna set, transmitting the first multiplexed signal via aplurality of neighboring frequency resources of an OFDM symbol of asecond antenna set, and transmitting the second multiplexed signal via aplurality of neighboring frequency resources of the OFDM symbol of thesecond antenna set, wherein the first multiplexed signal is transmittedon frequency resources that neighbor frequency resources that the secondmultiplexed signal is transmitted on.

Preferably, the first multiplexed signal and second multiplexed signalare respectively transmitted on two neighboring frequency resources.Preferably, the spreading factor is 2.

In one aspect of the invention, the first antenna set is space frequencyblock coded by applying a space frequency block code to each neighboringpair of frequency resources of one OFDM symbol, wherein the firstantenna set comprises two antennas. In another aspect of the invention,the second antenna set is space frequency block coded by applying aspace frequency block code to each neighboring pair of frequencyresources of one OFDM symbol, wherein the second antenna set comprisestwo antennas.

Preferably, the multiplexed signals transmitted via the first antennaset and the multiplexed signals transmitted via the second antenna setare transmitted via respectively different frequency resources.Preferably, the multiplexed signals transmitted via the first antennaset and the multiplexed signals transmitted via the second antenna setare transmitted via respectively different OFDM symbols.

In a further aspect of the invention, the first multiplexed signal andsecond multiplexed signal are transmitted alternately by the firstantenna set and second antenna set via independent frequency resourcesrepeatedly. Preferably, the first multiplexed signal and secondmultiplexed signal are transmitted a total of 3 times using the firstantenna set and second antenna set alternately.

In one aspect of the invention, the first antenna set comprises a firstantenna and a second antenna of a four-antenna group, and the secondantenna set comprises a third antenna and a fourth antenna of thefour-antenna group.

In another aspect of the invention, the first antenna set comprises afirst antenna and a third antenna of a four-antenna group, and thesecond antenna set comprises a second antenna and a fourth antenna ofthe four-antenna group.

In a further aspect of the invention, the first antenna set and secondantenna set respectively comprise one antenna.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. Features, elements, and aspects of the invention that arereferenced by the same numerals in different figures represent the same,equivalent, or similar features, elements, or aspects in accordance withone or more embodiments.

FIG. 1 illustrates an example of a conventional wireless (mobile)communication system.

FIG. 2A is a diagram explaining an example of a method for applying anSFBC/FSTD scheme in a mobile communication system in accordance with oneembodiment of the present invention.

FIG. 2B is a diagram explaining an example of a method for applying anSFBC/FSTD scheme to a spread signal in a mobile communication system inaccordance with one embodiment of the present invention.

FIGS. 3( a) and 3(b) are diagrams explaining an example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention.

FIGS. 4( a) and 4(b) are diagrams explaining another example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention.

FIGS. 5( a) and 5(b) are diagrams explaining another example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention.

FIGS. 6( a) and 6(b) are diagrams explaining another example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention.

FIGS. 7( a) and 7(b) are diagrams explaining another example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention.

FIGS. 8( a) and 8(b) are diagrams explaining a further example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention.

FIGS. 9( a) and 9(b) are diagrams explaining an example of atransmission structure applicable for repeatedly transmitting a spreadsignal in a mobile communication system in accordance with oneembodiment of the present invention.

FIGS. 10( a) and 10(b) are diagrams explaining another example of atransmission structure applicable for repeatedly transmitting a spreadsignal in a mobile communication system in accordance with oneembodiment of the present invention.

FIGS. 11( a) and 11(b) are diagrams explaining an example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention.

FIGS. 12( a) and 12(b) are diagrams explaining another example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention.

FIGS. 13( a)-13(c) are diagrams explaining an example of a method fortransmitting a spread signal via a plurality of OFDM symbols in a mobilecommunication system in accordance with one embodiment of the presentinvention.

FIGS. 14( a) and 14(b) are diagrams explaining an example of a methodfor transmitting a spread signal via a plurality of OFDM symbols in amobile communication system in accordance with one embodiment of thepresent invention in which an SFBC/FSTD scheme is applied to the spreadsignal.

FIG. 15 is a diagram explaining an example of a method for transmittinga spread signal in a mobile communication system in accordance with oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to transmitting a spread signal in awireless communication system.

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. It is to be understood that the following detailed descriptionof the present invention is exemplary and explanatory and is intended toprovide further explanation of the invention as claimed. The followingdetailed description includes details to provide complete understandingof the present invention. Yet, it is apparent to those skilled in theart that the present invention can be embodied without those details.For instance, predetermined terminologies are mainly used for thefollowing description, need not to be limited, and may have the samemeaning in case of being called arbitrary terminologies.

To avoid vagueness of the present invention, the structures or devicesknown in public are omitted or depicted as a block diagram and/orflowchart focused on core functions of the structures or devices.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

For the following embodiments, elements and features of the presentinvention are combined in prescribed forms. Each of the elements orfeatures should be considered as selective unless there is separate andexplicit mention. Each of the elements or features can be implementedwithout being combined with others. And, it is able to construct anembodiment of the present invention by combining partial elements and/orfeatures of the present invention. The order of operations explained inthe following embodiments of the present invention can be changed. Somepartial configurations or features of a prescribed embodiment can beincluded in another embodiment and/or may be replaced by correspondingconfigurations or features of another embodiment.

In this disclosure, embodiments of the present invention are describedmainly with reference to data transmitting and receiving relationsbetween a base station and a terminal. In this case, the base stationhas a meaning of a terminal node of a network, which directly performscommunication with the terminal. In this disclosure, a specificoperation described as performed by a base station can be carried out byan upper node of the base station. Namely, it is understood that variousoperations carried out by a network, which includes a plurality ofnetwork nodes including a base station, for the communication with aterminal can be carried out by the base station or other network nodesexcept the base station. “Base station” can be replaced by such aterminology as a fixed station, Node B, eNode B (eNB), access point andthe like. And, “terminal” can be replaced by such a terminology as UE(user equipment), MS (mobile station), MSS (mobile subscriber station)and the like.

Furthermore, antenna and time/frequency resource for transmittingsignals in a mobile communication system can be used in a manner ofbeing defined as a prescribed transmission structure. In the followingdescription, a transmission structure for antenna and frequency resourceis explained by considering a case that SFBC (space frequency blockcoding) scheme is applicable. Yet, the same method can be available fora transmission structure for antenna and time resource. And, it isunderstood that STBC (space time block coding) scheme is applicable tothe latter structure instead of SFBC.

FIG. 2A is a diagram explaining an example of a method for applying anSFBC/FSTD scheme in a mobile communication system, in accordance withone embodiment of the present invention. In FIG. 2A, a method forobtaining 4-degree transmitting antenna diversity is implemented using aplurality of transmitting antennas, e.g., four downlink transmittingantennas of a communication system. Here, two modulation signalstransmitted via two adjacent subcarriers are transmitted via a firstantenna set including two antennas by having space frequency blockcoding (SFBC) applied thereto. Two SFBC-coded subcarrier sets aretransmitted via two different antenna sets each including two differentantennas by having frequency switching transmit diversity (FSTD) appliedthereto. As a result, a transmitting antenna diversity degree 4 can beobtained.

Referring to FIG. 2A, a single small box indicates a single subcarriertransmitted via a single antenna. The letters “a”, “b”, “c” and “d”represent modulation symbols modulated into signals differing from eachother. Moreover, functions f₁(x), f₂(x), f₃(x) and f₄(x) indicate randomSFBC functions that are applied to maintain orthogonality between twosignals. These functions can be represented as in Formula 1.

f ₁(x)=x, f ₂(x)=r, f ₃(x)=−x*, f ₄(x)=x*  [Formula 1]

Despite two signals being simultaneously transmitted via two antennasthrough the random SFBC function applied to maintain orthogonalitybetween the two signals, a receiving side may be able to obtain anoriginal signal by decoding each of the two signals. In particular, FIG.2A shows a structure that SFBC and FSTD transmitted in downlink within arandom time unit is repeated. By applying a simple reception algorithmthat the same SFBC decoding and FSTD decoding are repeated in areceiving side through the structure of SFBC and FSTD repeatingtransmissions, decoding complexity is reduced and decoding efficiency israised.

In the example shown in FIG. 2A, modulated symbol sets (a, b), (c, d),(e, f) and (g, h) become an SFBC-coded set, respectively. FIG. 2A showsthat subcarriers having SFBC/FSTD applied thereto are consecutive.However, the subcarriers having SFBC/FSTD applied thereto may notnecessarily be consecutive in a frequency domain. For instance, asubcarrier carrying a pilot signal can exist between SFBC/FSTD appliedsubcarriers. Yet, two subcarriers constructing an SFBC coded set arepreferably adjacent to each other in a frequency domain so that wirelesschannel environments covered by a single antenna for two subcarriers canbecome similar to each other. Hence, when SFBC decoding is performed bya receiving side, it is able to minimize interference mutually affectingthe two signals.

In accordance with one embodiment of the present invention, an SFBC/FSTDscheme may be applied to a spread signal sequence. In a manner ofspreading a single signal into a plurality of subcarriers through(pseudo) orthogonal code in a downlink transmission, a plurality ofspread signals may be transmitted by a code division multiplexing (CDM)scheme. In the following description, a signal sequence spread by aprescribed spreading factor is named a spread signal.

For example, when attempting to transmit different signals “a” and “b”,if the two signals are to be CDM-transmitted by being spread by aspreading factor (SF) 2, the signal a and the signal b are transformedinto spread signal sequences (a·c₁₁, a·c₂₁) and (b·c₁₂, bc₂₂) using(pseudo) orthogonal spreading codes of two chip lengths (c₁₁, c₂₁) and(c₁₂, c₂₂), respectively. The spread signal sequences are modulated byadding a·c₁₁+b·c₁₂ and a·c₂₁+bc₂₂ to two subcarriers, respectively.Namely, a·c₁₁+b·c₁₂ and a·c₂₁+bc₂₂ become modulated symbols,respectively. For clarity and convenience, the spread signal sequenceresulting from spreading the signal a by SF=N is denoted as a₁, a₂, . .. , a_(N). Furthermore, a plurality of spread signals can be multiplexedby code division multiplexing (CDM) and then transmitted.

FIG. 2B is a diagram explaining an example of a method for applying anSFBC/FSTD scheme to a spread signal in a mobile communication system, inaccordance with one embodiment of the present invention. In order todecode a signal spread over a plurality of subcarriers by despreading ina receiving side, as mentioned in the foregoing description, it ispreferable that each chip of a received spread signal sequence undergo asimilar wireless channel response. In FIG. 2B, four different signals a,b, c and d are spread by SF=4 and the spread signals are transmitted bySFBC/FSTD through four subcarriers explained in the foregoingdescription of FIG. 2A. Assuming that the function explained for theexample in Equation 1 is used as an SFBC function, a received signal ineach subcarrier can be represented as in Formula 2.

[Formula 2]

h₁(a₁+b₁+c₁+d₁)−h₂(a₂+b₂+c₂+d₂)*  Subcarrier 1

h₁(a₂+b₂+c₂+d₂)+h₂(a₁+b₁+c₁+d₁)*  Subcarrier 2

h₁(a₃+b₃+c₃+d₃)−h₂(a₄+b₄+c₄+d₄)*h₃(a₃+b₃+c₃+d₃)−h₄(a₄+b₄+c₄+d₄)*  Subcarrier3

h₁(a₄+b₄+c₄+d₄)+h₂(a₃+b₃+c₃+d₃)*h₃(a₄+b₄+C₄+d₄)+h₄(a₃+b₃+C₃+d₃)*  Subcarrier4

In Formula 2, h_(i) indicates fading undergone by an i^(th) antenna.Preferably, subcarriers of the same antenna undergo the same fading. Anoise component added to a receiving side may be ignored. And, a singlereceiving antenna preferably exists. In this case, spread sequencesobtained by a receiving side after completion of SFBC decoding and FSTDdecoding can be represented as in Formula 3.

(|h₁|²+|h₂|²)·(a₁+b₁+c₁+d₁),

(|h₁|²+|h₂|²)·(a₂+b₂+c₂+d₂),

(|h₃|²+|h₄|²)·(a₃+b₃+c₃+d₃),

(|h₃|²+|h₄|²)·(a₄+b₄+c₄+d₄)  [Formula 3]

Here, in order to separate the spread sequence obtained by the receivingside from the signals b, c and d by despreading with a (pseudo)orthogonal code corresponding to the signal a for example, the wirelesschannel responses for the four chips is preferably the same. However, ascan be observed from Formula 3, signals transmitted via differentantenna sets by FSTD are (|h₁|²+|h₂|²) and (|h₃|²+|h₄|²) and provideresults through different wireless channel responses, respectively.Thus, complete elimination of a different CDM-multiplexed signal duringdispreading is not performed.

Therefore, one embodiment of the present invention is directed to amethod of transmitting at least one spread signal in a communicationsystem, wherein each of at least one signal is spread by (pseudo)orthogonal code or the like with a spreading factor (SF), and whereinthe at least one spread signal is multiplexed by CDM and transmitted viathe same antenna set. FIGS. 3( a) and 3(b) are diagrams explaining anexample of a method for applying an SFBC/FSTD scheme to a spread signalin a communication system in accordance with one embodiment of thepresent invention. In the present embodiment, each of at least onesignal is spread by (pseudo) orthogonal code or the like with SF=4.Furthermore, the at least one spread signal is multiplexed andtransmitted by CDM, and the multiplexed signals are transmitted via thesame antenna set.

In FIGS. 3( a) and (b), when a total of four transmitting antennas areused, a first antenna set includes a first antenna and a second antenna.A second antenna set includes a third antenna and a fourth antenna. Inparticular, each of the first and second antenna sets is the antenna setfor performing SFBC coding, and an FSTD scheme is applicable between thetwo antenna sets. According to the present embodiment, assuming thatdata to be transmitted is carried by a single OFDM symbol, the signalspread with SF=4, as shown in FIGS. 3( a) and 3(b), can be transmittedvia four neighbor subcarriers of one OFDM symbol via the same SFBC-codedantenna set.

In FIG. 3( a), shown is a case where the spread signal transmitted viathe first antenna set is different from the spread signal transmittedvia the second antenna set. In FIG. 3( b), shown is a case where thespread signal transmitted via the first antenna set is repeatedlytransmitted via the second antenna set to obtain a 4-degree transmittingantenna diversity gain.

FIGS. 4( a) and 4(b) are diagrams explaining another example for amethod of applying an SFBC/FSTD scheme to a spread signal in acommunication system in accordance with one embodiment of the presentinvention. In FIGS. 4( a) and 4(b), like the embodiment shown in FIGS.3( a) and 3(b), each of at least one signal is spread by (pseudo)orthogonal code or the like with SF=4. The at least one spread signal ismultiplexed and transmitted by CDM, and the multiplexed signals aretransmitted via the same antenna set.

In FIGS. 4( a) and 4(b), unlike FIGS. 3( a) and 3(b), when a total offour transmitting antennas are used, a first antenna set includes afirst antenna and a third antenna. A second antenna set includes asecond antenna and a fourth antenna. Namely, compared to FIGS. 3( a) and3(b), FIGS. 4( a) and 4(b) show a case of using a different method forconstructing each antenna set but applying the same SFBC/FSTD scheme.Here, according to the present embodiment, the signal spread with SF=4can be transmitted via four neighbor subcarriers of one OFDM symbol viathe same SFBC-coded antenna set.

In FIG. 4( a), shown is a case where the spread signal transmitted viathe first antenna set is different from the spread signal transmittedvia the second antenna set. In FIG. 4( b), shown is a case where thespread signal transmitted via the first antenna set is repeatedlytransmitted via the second antenna set to obtain a 4-degree transmittingantenna diversity gain.

In accordance with one embodiment of the present invention, the sametransmission structure may be applied for different spreading factors.Notably, a system can use various spreading factors by considering atransport channel status, a traveling speed of terminal, a communicationenvironment and the like. According to the present embodiment, the sametransmission structure may be used for the various spreading factorsrather than separately using a specific transmission structure for aparticular spreading factor. Moreover, according to the presentembodiment, spread signals multiplexed by a CDM scheme to be transmittedvia N subcarriers are applicable even if spread by any spreading factorM smaller than N, and do not necessarily need to be spread by thespreading factor N.

For example, the transmission structure corresponding to a case wherethe spreading factor is SF=4 is applicable to various spreading factorsother than SF=4. Consequently, this lessens the complication of a systemand prevents increased signaling due to a transmission structure varyingaccording to a prescribed spreading factor.

FIGS. 5( a) and 5(b) are diagrams explaining another example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention. In FIGS. 5( a) and 5(b), an example of a case using atotal of four transmitting antennas is shown, wherein a first antennaset includes a first antenna and second antenna, and a second antennaset includes a third antenna and fourth antenna.

In particular, FIG. 5( a) illustrates a case where the spread signaltransmitted via the first antenna set is different from the spreadsignal transmitted via the second antenna set. FIG. 5( b) illustrates acase where the spread signal transmitted via the first antenna set isrepeatedly transmitted via the second antenna set. Here, as mentioned inthe foregoing description, a 4-degree transmitting antenna diversitygain is obtained.

In the present embodiment, at least one signal is spread by (pseudo)orthogonal code or the like by SF=2. Moreover, the at least one signalis CDM-multiplexed and transmitted. Preferably, the present embodimentprovides a method for transmitting the multiplexed signals according tothe same transmission structure defined by SF=4.

Referring to FIGS. 5( a) and 5(b), the spread signals CDM-multiplexedwith four subcarriers by SF=2 can be transmitted via two subcarriers,respectively. By applying the same transmission structure shown in FIG.3, an SFBC/FSTD transmission scheme can be applied to FIGS. 5( a) and5(b) by 4-neighbor subcarrier unit of FIGS. 3( a) and 3(b). However,unlike FIGS. 3( a) and 3(b), a signal can be transmitted via subcarrierin a manner that the CDM-multiplexed signal spread by SF=2 istransmitted by 2-subcarrier unit instead of the CDM-multiplexed signalspread by SF=4.

FIGS. 6( a) and 6(b) are diagrams explaining another example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention. FIGS. 6( a) and 6(b) differ from FIGS. 5( a) and 5(b)merely by the construction of the antenna set. Thus, the same method fortransmitting a spread signal shown in FIGS. 5( a) and 5(b) are appliedto FIGS. 6( a) and 6(b).

In FIGS. 6( a) and 6(b), at least one signal is spread by (pseudo)orthogonal code or the like by SF=2. The at least one signal isCDM-multiplexed and transmitted. Moreover, the present embodimentprovides a method for transmitting the multiplexed signals according tothe same transmission structure defined by SF=4.

Referring to FIG. 6, the spread signals CDM-multiplexed with foursubcarriers by SF=2 can be transmitted via two subcarriers,respectively. By applying the same transmission structure shown in FIGS.4( a) and 4(b), an SFBC/FSTD transmission scheme can be applied to FIGS.6( a) and 6(b) by 4-neighbor subcarrier unit of FIGS. 4( a) and 4(b).However, unlike FIGS. 4( a) and 4(b), a signal can be transmitted viasubcarrier in a manner that the CDM-multiplexed signal spread by SF=2 istransmitted by 2-subcarrier unit instead of the CDM-multiplexed signalspread by SF=4.

Preferably, FIGS. 5( a) and 5(b) and 6(a) and 6(b) illustrateembodiments of the present invention applicable to any M or N thatsatisfies the equation M 5. N. Preferably, the present embodiment isapplicable to an SFBC transmission using two transmitting antennas or atransmission using a single transmitting antenna.

FIGS. 7( a) and 7(b) are diagrams explaining another example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention. In FIGS. 7( a) and 7(b), an SFBC transmission usingtwo transmitting antennas is shown. FIG. 7( a) illustrates atransmission structure for transmitting spread signals CDM-multiplexedwith 4 subcarriers by SF=4 via four subcarriers. FIG. 7( b) illustratesa transmission structure for transmitting spread signals CDM-multiplexedwith 4 subcarriers by SF=2 via two subcarriers each.

In FIG. 7( b), data is preferably carried by subcarriers in a mannerthat the CDM-multiplexed signals spread by SF=2 instead of theCDM-multiplexed signals spread by SF=4 are transmitted by 2-subcarrierunit each. This occurs even though the SFBC transmission scheme isapplied by 4-neighbor subcarrier unit as in the transmission structureof FIG. 7( a), wherein the spread signals are spread by SF=4 accordingto the present embodiment.

FIGS. 8( a) and 8(b) are diagrams explaining a further example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention. In FIGS. 8( a) and 8(b), a transmission uses a singletransmitting antenna. FIG. 8( a) illustrates a transmission structurefor transmitting spread signals CDM-multiplexed with 4 subcarriers bySF=4 via four subcarriers. FIG. 8( b) illustrates a transmissionstructure for transmitting spread signals CDM-multiplexed with 4subcarriers by SF=2 via two subcarriers each.

In FIG. 8( b), data is preferably carried by subcarriers in a mannerthat the CDM-multiplexed signals spread by SF=2 instead of theCDM-multiplexed signals spread by SF=4 are transmitted by 2-subcarrierunit each. This occurs even though the SFBC transmission scheme isapplied by 4-neighbor subcarrier unit as in the transmission structureof FIG. 8( a), wherein the spread signals are spread by SF=4 accordingto the present embodiment.

Preferably, FIGS. 7( a) and 7(b) and 8(a) and 8(b) illustrateembodiments of the present invention applicable to any M or N thatsatisfies the equation M≦N. Preferably, by applying the presentembodiment to a system capable of using 1, 2 or 4 transmitting antennasselectively, it is advantageous for random CDM signals or CDM signalgroups to be allocated to a consistent structure by N-subcarrier unit,e.g., 4-subcarrier unit.

In accordance with another embodiment of the present invention, a spreadsignal may be repetitively transmitted. Particularly, differentsubcarriers may be repeatedly transmitted at least one time on afrequency axis, i.e., for a period of the same time unit, such that asame signal is repeatedly transmitted to obtain additional diversity.

FIGS. 9( a) and 9(b) are diagrams explaining an example of atransmission structure applicable for repeatedly transmitting a spreadsignal in a mobile communication system in accordance with embodiment ofthe present invention. Referring to FIGS. 9( a) and 9(b), anantenna-frequency mapping structure can be repeated with a prescribednumber of subcarrier intervals. In particular, FIGS. 9( a) and 9(b)illustrate a repetitive transmission by 8-subcarrier unit, for example.By applying the SFBC/FSTD scheme through the eight neighbor subcarriers,4-degree transmission antenna diversity gain may be obtained.Preferably, the repetition unit constructed with eight subcarriers inFIGS. 9( a) and 9(b) include four subcarriers for carrying a spreadsignal spread by SF=4 via a first antenna set and four subcarriers forcarrying a spread signal spread by SF=4 via a second antenna set.

Here, each of the spread signals may be a different signal or arepetitively transmitted signal. In case that each of the spread signalsis a different signal, FIGS. 9( a) and 9(b) show that each spread signalis repeatedly transmitted three times. In case that each of the spreadsignals is a repetitively transmitted signal, FIGS. 9( a) and 9(b) showthat each spread signal is repeatedly transmitted a total of six times.Moreover, if each of the spread signals is a different signal, spacediversity gain can be obtained by applying antenna set mapping of asecond repetition unit different from a first repetition unit.

Notably, FIGS. 9( a) and 9(b) differ from each other with regard toantenna construction of the first and second antenna sets. However, thepresent embodiment may be applied to FIGS. 9( a) and 9(b) in the samemanner.

FIGS. 10( a) and 10(b) are diagrams explaining another example of atransmission structure applicable for repeatedly transmitting a spreadsignal in a mobile communication system in accordance with oneembodiment of the present invention. FIGS. 10( a) and 10(b) show amethod of transmitting a signal spread by SF=2 using the sametransmission structure shown in FIGS. 9( a) and 9(b).

Referring to FIGS. 10( a) and 10(b), like FIGS. 9( a) and 9(b), anantenna-frequency mapping structure can be repeated with a prescribednumber of subcarrier intervals. In particular, FIGS. 10( a) and 10(b)show a repetitive transmission by 8-subcarrier unit, for example. Byapplying the SFBC/FSTD scheme through the eight neighbor subcarriers, a4-degree transmission antenna diversity gain may be obtained.

In FIGS. 10( a) and 10(b), two spread signals spread by SF=2 may betransmitted each using the same four subcarriers used to transmit asingle spread signal spread by SF=4 in FIGS. 9( a) and 9(b). Inparticular, the repetition unit constructed with eight subcarriersincludes four subcarriers for carrying the two spread signals spread bySF=2 via the first antenna set and four subcarriers for carrying thespread signals spread by SF=2 each via the second antenna set accordingto the above-mentioned embodiment. Preferably, each of the spreadsignals may be a different signal or a repetitively transmitted signal.Moreover, antenna set mapping may be differently applied per repetitionunit.

Notably, FIGS. 10( a) and 10(b) differ from each other with regard toantenna construction of the first and second antenna sets. However, thepresent embodiment may be applied to FIGS. 10( a) and 10(b) in the samemanner.

In accordance with another embodiment of the present invention,allocated resources may be partially used according to a transmissionstructure. Particularly, allocated resources may be used partiallyaccording to a transmission structure instead of using all resources totransmit a spread signal according to a preset transmission structure.

FIGS. 11( a) and 11(b) are diagrams explaining an example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention. In FIGS. 11( a) and 11(b), a spread signal spread bySF=4 is transmitted, wherein an antenna set is determined by4-subcarrier unit to enable a spread signal to be transmitted via thesame antenna set.

Referring to FIGS. 11( a) and 11(b), transmission may be performed usingfour of eight subcarriers allocated by a first repetition unit accordingto a transmission structure instead of using all allocated resources.Moreover, transmission may be performed using four of eight subcarriersallocated by a second repetition unit. In doing so, an antenna setdifferent from that of a previous transmission may be used to implementan SFBC/FSTD scheme for obtaining 4-degree transmission antennadiversity. Preferably, as mentioned in the foregoing description, eachof the repetition units is allocated to have a prescribed number ofsubcarrier intervals.

In accordance with the present embodiment, the repetition unitconstruction does not include eight neighbor subcarriers. Instead, foursubcarriers include neighbor subcarriers, in which a prescribed numberof subcarrier intervals are inserted. And, the rest of the subcarriersinclude neighbor subcarriers. Thus, frequency diversity in addition to4-degree antenna diversity may be obtained.

In FIGS. 11( a) and 11(b), four subcarriers each are configured toinclude neighbor subcarriers by considering an advantage thatsubcarriers carrying a single spread signal include subcarriersneighboring each other. Hence, the number of subcarriers includingneighbor subcarriers can be freely modified according to the number ofsubcarriers used for spread signal transmission according to a spreadingfactor or other reasons, purposes or the like.

Notably, FIGS. 11( a) and 11(b) differ from each other with regard toantenna construction of the first and second antenna sets. However, thepresent embodiment may be applied to FIGS. 11( a) and 11(b) in the samemanner.

FIGS. 12( a) and 12(b) are diagrams explaining another example of atransmission structure applicable for transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention. FIGS. 12( a) and 12(b) show a method for transmittinga spread signal spread by SF=2 using the same transmission structureshown in FIGS. 11( a) and 11(b).

Referring to FIGS. 12( a) and 12(b), like FIGS. 11( a) and 11(b), atransmission may be performed using four of eight subcarriers allocatedby a first repetition unit according to a transmission structure insteadof using all allocated resources. Moreover, a transmission may beperformed using four of eight subcarriers allocated by a secondrepetition unit. In doing so, an antenna set different from that of aprevious transmission may be used to implement an SFBC/FSTD scheme forobtaining 4-degree transmission antenna diversity. Preferably, asmentioned in the foregoing description, each of the repetition units isallocated to have a prescribed number of subcarrier intervals.

However, unlike the embodiment shown in FIGS. 11( a) and 11(b), FIGS.12( a) and 12(b) illustrate transmitting a spread signal spread by SF=2,in which two spread signals spread by SF=2 can be transmitted using foursubcarriers used to transmit a single spread signal spread by SF=4. Eachof the spread signals may be a different signal or a repetitivelytransmitted signal. Moreover, antenna set mapping may be applieddifferently per repetition unit.

In accordance with the present embodiment, the repetition unitconstruction does not include eight neighbor subcarriers. Instead, foursubcarriers include neighbor subcarriers, in which a prescribed numberof subcarrier intervals are inserted. And, the rest of the subcarriersinclude neighbor subcarriers.

Notably, FIGS. 12( a) and 12(b) differ from each other with regard toantenna construction of the first and second antenna sets. However, thepresent embodiment may be applied to FIGS. 12( a) and 12(b) in the samemanner.

Compared to the method described with reference to FIGS. 6( a) and 6(b),the embodiment of FIGS. 12( a) and 12(b) saves considerable resourcesrequired for repetitive transmission by reducing additionally usedresources in half. Therefore, by applying the repetitive transmissionaccording to the present embodiment, resources for data transmission areused more efficiently.

In accordance with another embodiment of the present invention, aplurality of OFDM symbols may be applied. As described above, anSFBC/FSTD scheme was applied for a single time unit according to anembodiment of the present invention. However, transmitting a signalusing a plurality of time units may be considered. In the followingdescription, a single OFDM symbol is defined as a time unit in acommunication system adopting orthogonal frequency divisionmultiplexing. Accordingly, a method for transmitting a signal using aplurality of OFDM symbols is explained as follows.

When transmitting via a plurality of OFDM symbols, repetitivetransmission on a time axis as well as a frequency axis is possible toobtain diversity in addition to transmitting antenna diversity.Specifically, in the following description, exemplarily described is acase where CDM and SFBC/FSTD schemes are applied to a spread signal foran ACK/NAK signal transmitted in downlink to announce thesuccessful/failed reception of data transmitted in uplink.

FIGS. 13( a)-13(c) are diagrams explaining an example of a method fortransmitting a spread signal via a plurality of OFDM symbols in a mobilecommunication system in accordance with one embodiment of the presentinvention. Referring to FIGS. 13( a)-13(c), each small box indicates aresource element (RE) constructed with a single OFDM symbol and a singlesubcarrier. A_(ij) may indicate and ACK/NAK signal multiplexed by CDM,wherein i indicates an index of a multiplexed signal after spreading,and j indicates an ACK/NAK channel index of the multiplexed ACK/NAKsignal. Here, the ACK/NAK channel indicates a set of multiplexed ACK/NAKsignals. Moreover, there can exist a plurality of ACK/NAK channelsaccording to a necessity and resource situation of each system. Forclarity and convenience of description, a single ACK/NAK channel existsin FIGS. 13( a)-13(c).

In FIG. 13( a), shown is an example where a multiplexed ACK/NAK signalis transmitted via a single OFDM symbol. Preferably, four ACK/NAKsignals are spread by a spreading factor SF=4 for a single OFDM symbol,multiplexed by CDM, and then transmitted via four neighbor subcarriers(A₁₁, A₂₁, A₃₁, A₄₁). Because a single OFDM symbol is used for theACK/NAK signal transmission, diversity gain on a time axis for theACK/NAK signal transmission may not be obtained. However, fourrepetitive transmissions of the ACK/NAK signal multiplexed by CDM alonga frequency axis may be performed. Accordingly, the four-time repetitionfacilitates diversity via repetition, wherein a repetition count variesaccording to a channel status and/or a resource status of the system.

In FIG. 13( b), shown is an example where a multiplexed ACK/NAK signalis transmitted via a plurality of OFDM symbols. Referring to FIG. 13(b), four ACK/NAK signals are spread by a spreading factor SF=4 for twoOFDM symbols each, multiplexed by CDM, and then transmitted via fourneighbor subcarriers. Preferably, when OFDM symbols for ACK/NAK signaltransmission increase, the ACK/NAK signal used for a single OFDM symbolmay be repetitively used for the increased OFDM symbols as it is.However, when the ACK/NAK signal is repetitively transmitted for asecond OFDM symbol, transmission is performed to maximize use ofsubcarriers that are not overlapped with former subcarriers used for afirst OFDM symbol. This is preferable when considering a frequencydiversity effect.

In FIG. 13( b), the number of ACK/NAK signals transmittable despite theincreased number of OFDM symbols is equal to the case of using a singleOFDM symbol. According to the present embodiment, an ACK/NAK signal,which was repeated on a frequency axis only when using a single OFDMsymbol, can be transmitted using more time-frequency resources fortransmitting the same number of ACK/NAK signals by substantiallyincrementing the repetition count of time-frequency. Here, because OFDMsymbols used for the ACK/NAK transmission are increased, more signalpower used for the ACK/NAK transmission can be allocated. Hence, theACK/NAK signal may be transmitted to a cell having a wider area.

In FIG. 13( c), shown is another example where a multiplexed ACK/NAKsignal is transmitted via a plurality of OFDM symbols. Referring to FIG.13( c), when the number of OFDM symbols for ACK/NAK signal transmissionis incremented to 2, transmission may be performed by reducing thefrequency-axis repetition count of the ACK/NAK signal multiplexed byCDM. Thus, by performing the transmission by decreasing the repetitioncount when the number of OFDM symbols is incremented to 2, resources areefficiently utilized.

Compared to the transmission method shown in FIG. 13( b), four-timefrequency-axis repetitions of ACK/NAK signal are reduced to two-timerepetitions in FIG. 13( c). However, because the number of OFDM symbolsused for ACK/NAK signal transmission is incremented, compared with thecase of using a single OFDM symbol in FIG. 13( a), FIG. 13( c) is nodifferent in that four time-frequency resource areas are available.

Compared to the method shown in FIG. 13( b), the method of FIG. 13( c)shows that signal power for ACK/NAK channel transmission may be reducedbecause the number of time-frequency resource areas used for a singleACK/NAK channel transmission is reduced. However, because the ACK/NAKchannel is transmitted across the time-frequency areas, per-symboltransmission power allocation may be performed more efficiently than thecase of transmitting via a single OFDM symbol only.

In case that ACK/NAK signals are repetitively transmitted in the samestructure for all OFDM symbols to simplify a scheduling operation on asystem, e.g., the time-frequency resources shown in FIG. 13( b) areused, different ACK/NAK channels may be transmitted. In particular,because twice as many ACK/NAK channels may be transmittable, resourcesare more efficiently used.

Preferably, a spreading factor for multiplexing a plurality of ACK/NAKsignals, a repetition count in time-frequency domain, and the number ofOFDM symbols for ACK/NAK signal transmission, which are explained withreference to FIGS. 13( a)-13(c), are exemplarily provided for a moreaccurate description of the present invention. It is understood thatdifferent spreading factors, different repetition counts and variousOFDM symbol numbers are applicable to the present invention. Moreover,the embodiment shown in FIGS. 13( a)-13(c) relate to using a singletransmitting antenna not using transmitting antenna diversity, but isalso applicable to a 2-transmitting antenna diversity method, a4-transmitting antenna diversity method, and the like.

FIGS. 14( a) and 14(b) are diagrams explaining an example of a methodfor transmitting a spread signal via a plurality of OFDM symbols in amobile communication system in accordance with one embodiment of thepresent invention, wherein an SFBC/FSTD scheme is applied to the spreadsignal. Preferably, an embodiment for implementing a 4-degreetransmitting antenna diversity effect using a total of four transmittingantennas is explained with reference to FIGS. 14( a) and 14(b). Forclarity and convenience of description, a single ACK/NAK channel exists.

In FIG. 14( a), an SFBC/FSTD scheme is applied to a spread signal usingfour transmitting antennas and the signal is transmitted for a pluralityof OFDM symbols. Four ACK/NAK signals are spread by a spreading factorSF=4 for two OFDM symbols each, multiplexed by CDM, and then transmittedvia four neighbor subcarriers. Preferably, when OFDM symbols for ACK/NAKsignal transmission increase, the ACK/NAK signal used for a single OFDMsymbol may be repetitively used for the increased OFDM symbols as it is.This is similar to the process described with reference to FIG. 13 (b).

However, when a repetitive transmission is carried out for a second OFDMsymbol, transmission is performed using an antenna set different from anantenna set used for a first OFDM symbol. For example, if a transmissionfor a first OFDM symbol is performed using a first antenna set includinga first antenna and third antenna, a transmission for a second OFDMsymbol may be performed using a second antenna set including a secondantenna and fourth antenna. Preferably, transmission is performed tomaximize use of subcarriers that are not overlapped with formersubcarriers used for the first OFDM symbol. This is preferable whenconsidering a frequency diversity effect.

In FIG. 14( b), shown is another example of applying an SFBC/FSTD schemeto a spread signal using four transmitting antennas and transmitting thesignal for a plurality of OFDM symbols. Preferably, when the number ofOFDM symbols for ACK/NAK signal transmission is incremented to 2, thesignal may be transmitted by reducing a frequency-axis repetition countof the ACK/NAK signal multiplexed by CDM. This is similar to the processdescribed with reference to FIG. 13( c). However, when repetitivetransmission is performed for a second OFDM symbol, the transmissionwill be carried out using an antenna set different from an antenna setused for the first OFDM symbol.

In the above description of the examples shown in FIGS. 13( a)-13(c) and14(a) and 14(b), the signal spread by SF=4 is transmitted via at leastone OFDM symbol only. However, the present embodiment is applicable to acase of using several OFDM symbols in case of a spreading factor SF=2.Preferably, for the spreading factor SF=2, two spread signals spread bySF=2 are transmitted each using two of four subcarriers allocated totransmit a spread signal spread by SF=4. Alternatively, a two-timerepetition method is applicable thereto.

In case of transmission via several OFDM symbols, repetition on a timeaxis as well as a frequency axis is applicable to obtain diversity inaddition to transmitting antenna diversity. The above embodiments areprovided to explain the applications of the present invention and arealso applicable to a system using an SFBC/FSTD transmission diversitymethod regardless of various spreading factors (SF), various OFDM symbolnumbers and repetition counts on time and frequency axes.

FIG. 15 is a diagram explaining an example of a method for transmittinga spread signal in a mobile communication system in accordance with oneembodiment of the present invention. Referring to FIG. 15, a firstsignal is spread using a plurality of spreading codes, wherein theplurality of spreading codes have a spreading factor (S1502). The firstspread signal is multiplexed by code division multiplexing (S1504).Similarly, a second signal is spread using a plurality of spreadingcodes, wherein the plurality of spreading codes have a spreading factor(S1506). The second spread signal is multiplexed by code divisionmultiplexing (S1508). The first and second multiplexed signals aretransmitted, wherein the first multiplexed signal is transmitted onfrequency resources that neighbor frequency resources that the secondmultiplexed signal is transmitted on (S1510). The first and secondmultiplexed signals are transmitted via frequency resources of an OFDMsymbol of a first antenna set and a second antenna set. A method ofreceiving a spread signal is performed inversely.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

Embodiments of the present invention can be implemented by variousmeans, e.g., hardware, firmware, software, and any combination thereof.In case of the implementation by hardware, a method of transmitting aspread signal in a communication system according to one embodiment ofthe present invention can be implemented by at least one of applicationspecific integrated circuits (ASICs), digital signal processors (DSPs),digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays (FPGAs), a processor, acontroller, a microcontroller, a microprocessor, etc.

In case of implementation by firmware or software, a method oftransmitting a spread signal in a communication system according to oneembodiment of the present invention can be implemented by a module,procedure, function and the like capable of performing the abovementioned functions or operations. Software code is stored in a memoryunit and can be driven by a processor. The memory unit is providedwithin or outside the processor to exchange data with the processor byvarious means known in public.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses. Thedescription of the present invention is intended to be illustrative, andnot to limit the scope of the claims. Many alternatives, modifications,and variations will be apparent to those skilled in the art. In theclaims, means-plus-function clauses are intended to cover the structuredescribed herein as performing the recited function and not onlystructural equivalents but also equivalent structures.

1. An apparatus configured to transmit a spread signal in a mobilecommunication system, the apparatus comprising: a plurality of antennas;a radio frequency unit; and a processor, wherein the processor isconfigured to: spread a first signal using a plurality of spreadingcodes, having a spreading factor, multiplex the first spread signal bycode division multiplexing, transmit the first multiplexed signal via aplurality of neighboring frequency resources of an orthogonal frequencydivision multiplexing (OFDM) symbol of a first antenna set, spread asecond signal using a plurality of spreading codes, having a spreadingfactor, multiplex the second spread signal by code divisionmultiplexing, transmit the second multiplexed signal via a plurality ofneighboring frequency resources of the OFDM symbol of the first antennaset, transmit the first multiplexed signal via a plurality ofneighboring frequency resources of an OFDM symbol of a second antennaset, and transmit the second multiplexed signal via a plurality ofneighboring frequency resources of the OFDM symbol of the second antennaset, wherein the first multiplexed signal is transmitted on frequencyresources that neighbor frequency resources on which the secondmultiplexed signal is transmitted.
 2. The apparatus of claim 1, whereinthe first multiplexed signal and the second multiplexed signal arerespectively transmitted on two neighboring frequency resources.
 3. Theapparatus of claim 1, wherein the spreading factor is
 2. 4. Theapparatus of claim 1, wherein the first antenna set is a space frequencyblock coded by applying a space frequency block code to each neighboringpair of frequency resources of one OFDM symbol.
 5. The apparatus ofclaim 4, wherein the first antenna set comprises two antennas.
 6. Theapparatus of claim 1, wherein the second antenna set is a spacefrequency block coded by applying a space frequency block code to eachneighboring pair of frequency resources of one OFDM symbol.
 7. Theapparatus of claim 6, wherein the second antenna set comprises twoantennas.
 8. The apparatus of claim 1, wherein the multiplexed signalstransmitted via the first antenna set and the multiplexed signalstransmitted via the second antenna set are transmitted via respectivelydifferent frequency resources.
 9. The apparatus of claim 1, wherein themultiplexed signals transmitted via the first antenna set and themultiplexed signals transmitted via the second antenna set aretransmitted via respectively different OFDM symbols.
 10. The apparatusof claim 1, wherein the first multiplexed signal and the secondmultiplexed signal are transmitted alternately by the first antenna setand the second antenna set via independent frequency resourcesrepeatedly.
 11. The apparatus of claim 10, wherein the first multiplexedsignal and the second multiplexed signal are transmitted a total ofthree times using the first antenna set and the second antenna setalternately.
 12. The apparatus of claim 1, wherein the first antenna setcomprises a first antenna and a second antenna of a four-antenna group.13. The apparatus of claim 12, wherein the second antenna set comprisesa third antenna and a fourth antenna of the four-antenna group.
 14. Theapparatus of claim 1, wherein the first antenna set comprises a firstantenna and a third antenna of a four-antenna group.
 15. The apparatusof claim 14, wherein the second antenna set comprises a second antennaand a fourth antenna of the four-antenna group.
 16. The apparatus ofclaim 1, wherein the first antenna set and the second antenna setrespectively comprise one antenna.
 17. The apparatus of claim 1, whereinthe first signal and the second signal are ACK/NACK signals forindicating whether uplink data is successfully received.